what makes this platform know when to turn
import greenfoot.*; // (World, Actor, GreenfootImage, and Greenfoot) public class Platform extends Actor { private int speed = 4; private int leftTurn = 270; private int rightTurn = 480; public void act() { setLocation ( getX() + speed, getY() ); Actor actor = getOneIntersectingObject(null); if(actor != null) { actor.setLocation ( actor.getX() + speed, actor.getY() ); } if (atTurningPoint()) { speed = -speed; } } public boolean atTurningPoint() { return (getX() <= leftTurn || getX() >= rightTurn); } }